Developing green roofs

Green roofs and building facades can be built on new buildings and retrofitted on existing ones, especially in urban areas where there are few other opportunities for adding green infrastructure.

The Muse family home in London incorporates many green features, including a green roof. Photo by Jefferson Smith/Bere architects

Green roofs can have a variety of climate-related benefits, depending on the type of roof used. They contribute to:

evaporative cooling, improving the microclimate of surrounding areas

shade for buildings, preventing solar gain and helping with passive cooling in summer and reducing demand for air conditioning

insulation to buildings, preventing heat loss in winter

alternative habitats for some species, helping them adapt to changes

reducing the rate and volume of surface water run-off

providing public or private amenity space

extending the lifespan of the roof membrane

reducing noise levels

There are three categories of green roofs according to their use, construction method and maintenance requirements: (English Nature, 2003).

intensive green roofs are often referred to as roof gardens. Equivalent to gardens and parks at ground level, they may include lawns, beds, shrubs, trees, and water features. Normally accessible to people, but this may be as private rather than public green space. Require regular maintenance including irrigation. They have deep soil layers, of at least 15 cm, and therefore place the highest demands on the building structure. Typically installed where the slope is less than 10º.

simple intensive green roofs consist of lawns or ground covering plants. Require regular maintenance, including irrigation, but make fewer demands on the building structure than intensive green roofs.

extensive green roofs are normally vegetated with mosses, succulents, herbs or grasses and are intended to be self-sustaining with minimal maintenance and no irrigation. Not normally designed to be accessible. May be flat or sloping, and angles can be as much as 45º. The substrate is typically thin. Where the growing medium is deeper, and hence a more diverse range of plants can be grown, they are sometimes referred to as semi-extensive.

Green roofs and building facades are a useful way to add greenery on otherwise ‘wasted’ spaces. Local Development Frameworks should recognise their role and encourage their sensitive introduction as appropriate. They can be added to new buildings and retrofitted on existing ones, especially in areas where there are few other opportunities for adding green infrastructure to the urban form. Designs need to cater for a range of functions, including recreation on larger roofs. The Living Roofs website provides a large body of guidance and examples of the design and management of such roofs.

Stuttgart is a good example of a city with a successful initiative supporting green roofs. The City authority requires green roofs on all new flat-roofed industrial buildings as a planning requirement. Rather than implement such as policy, Vienna has sought to stimulate the market through providing subsidies and grants for new green roofs at the stages of planning application, installation and 3 years post construction to ensure ongoing maintenance.

Vertical habitats need to be carefully considered in building and site design. They can provide a number of benefits in terms of microclimate, ecology and aesthetics. However, their water resource demands should be investigated and limited to rain water-fed systems where possible to ensure good water management practice